1. Field of the Invention
This invention relates to an original reader apparatus which controls the drive timing of a stepping motor for moving a carriage including a fluorescent lamp, an optical system, a photoelectric converter and the like, in the sub-scanning direction, i.e., along the axis perpendicular to that along which the photoelectric converter reads the original.
2. Description of the Related Art
An original reader apparatus reads an original placed on an original table by moving a carriage on which an original scanning section is mounted. The original scanning section includes a fluorescent lamp, an optical system, a photoelectric converter, and the like. The fluorescent lamp irradiates an original, the light reflected by the original or transmitted therethrough travels via the optical system comprising an optical focusing lens to the photoelectric converter constituted by a CCD line image sensor.
The carriage having the optical system and the like is moved in the sub-scanning direction, i.e., along the axis perpendicular to that along which the photo electric converter reads the original, by a stepping motor which operates in response to a cock signal supplied from a CPU (Central Processing Unit) during an acceleration operation, and operates in synchronism with a 1-line synchronization timing signal during a constant speed operation. When the driving of the stepping motor is changed from an acceleration operation to a constant speed operation, the drive timing may deviate. If this occurs, the acceleration operation cannot be changed smoothly to the constant speed operation, thereby causing vibration of the carriage and step out of the stepping motor.
If the stepping motor is accelerated in synchronism with a 1-line synchronization timing signal, the drive timing in an acceleration operation may change abruptly, (i.e., the pulse width may be reduced abruptly), making smooth acceleration impossible.